Updated: 4:26pm UK, Saturday 10 May 2014
Splitting the captured Nigerian schoolgirls into groups by their kidnappers is "standard operating procedure", a hostage negotiator has told Sky News.
Dr James Alvarez explained this was done on the basis of "not putting all your eggs in one basket".
He also said while negotiation was the safest option, it often had to be backed up by the threat of force in order to act as a back-up if talks do not work out, and also as a "prod" to the hostage-takers.
Meanwhile, Davis Lewin from the Henry Jackson Society - a think-tank on extremism - gave a chilling insight into the Boko Haram militant group behind the kidnappings.
Mr Lewin told Sky News the movement had a "gruesome history" and posed a "major security threat".
They demonstrated "a brutality that frankly doesn't compute in Western minds", he said.
It is thought the schoolgirls are being held in a forest near the border with Cameroon.
Their kidnappers have divided the girls into at least four different groups, complicating the search and hampering rescue efforts.
Dr Alvarez said: "It's standard operating procedure. You don't want to put all your eggs in one basket."
He said negotiators would be making contacts locally and trying to gather information about the aims of the group, what they wanted with the girls, and also find out from the Nigerian government what concessions they are prepared to make.
"Negotiations only work if you have got something to exchange," he said.
Mr Lewin added: "What the problem really is, is that there's a very grave lack of infrastructure in terms of intelligence in terms of capability on the part of the Nigerian government in the region of the country where these extremists are active.
"We have seen them get stronger and stronger and they have really proven to be one of the most deadly forms of this radical Islamist threat with thousands dead, and a brutality that frankly doesn't compute in Western minds.
"The leader of this terrorist movement couldn't care less about the outrage that Michelle Obama and so many others have expressed."